An optical network adopting a WDM (Wavelength Division Multiplex) system in the related art is designed to make the most of a resource (such as a bandwidth of an optical line) at the start of operation. As time passes, however, the network usually experiences a situation where the resource is not used to the fullest due to the change in distribution of a demand from a client, the change in network topology, or equipment failure, for example. Under such situation, it is effective for a network design apparatus to re-optimize the network by redesigning the network that is once optimized.
The network design apparatus in the attempt to re-optimize the network allocates the demand to each time slot (hereinafter simply referred to as a “slot”) of the optical line in a way different from the previous way. There is a possibility that the allocation causes communication interruption in the network in operation when the allocation of the demand to the slot is cancelled (hereinafter referred to as “demand cancellation” as needed) without preparing a substitute optical line in advance. Being a factor of interrupting a service provided by a telecommunications carrier, the communication interruption is desirably avoided as much as possible.
Patent Document 1: Japanese Laid-open Patent Publication No. 2012-199644
However, the aforementioned network design has had a problem as follows. That is, the network design apparatus in the related art has performed the allocation to the slot without considering the procedure of changing each demand in re-optimizing the network. The network design apparatus has therefore been unable to derive a procedure by which the network can be re-optimized without performing the demand cancellation (hereinafter referred to as a “best procedure”) in a short period of time when such procedure is available. Moreover, the network design apparatus has been unable to derive, in a short period of time, a procedure by which the network can be re-optimized with the smallest number of demand cancellations (hereinafter referred to as a “second best procedure”) when the best procedure is not available. These have been the factors of inhibiting the procedure that is effective in efficiently re-optimizing the network from being promptly presented to a user.